PROBE, a batch-mode information retrieval program used to search the Educational Resources Information Center (ERIC) data base, was developed by Indiana University. To evaluate the effectiveness of the program, questionnaires were given to the users of 200 consecutive searches during February 1973. Relevance ratios were computed by comparing the number of documents considered useful by the user to the number retrieved. For searches using ERIC descriptors, the average relevance ratio was 54.7%. For searches using natural language, it was 42%. It was found that the cost of a descriptor search was $14.42 when 150 searches were run each month and $9.18 per search when 300 searches were run. The cost of abstract searches was $22.25 for 150 searches per month and $17.01 for 300 per month. Based on these findings and a separate user study, it was concluded that the PROBE service was satisfying the user and was cost-effective in that it could become self-supporting at a nominal fee. (Author/PF)